Silicon-based energy storage devices with cyclic carbonate containing electrolyte additives

ABSTRACT

Electrolytes and electrolyte additives for use in energy storage devices, comprising cyclic carbonate compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.application Ser. No. 16/213,834 filed Dec. 7, 2018, pending (nowallowed), which claims the benefit of U.S. Provisional Application No.62/596,034, filed Dec. 7, 2017. The entirety of the above referencedapplications are hereby incorporated by reference.

BACKGROUND Field

The present application relates generally to electrolytes for energystorage devices. In particular, the present application relates toelectrolytes and additives for use in lithium-ion energy storage deviceswith silicon-based anode materials.

Description of the Related Art

As the demands for both zero-emission electric vehicles and grid-basedenergy storage systems increase, lower costs and improvements in energydensity, power density, and safety of lithium (Li)-ion batteries arehighly desirable. Enabling the high energy density and safety of Li-ionbatteries requires the development of high-capacity, and high-voltagecathodes, high-capacity anodes and accordingly functional electrolyteswith high voltage stability, interfacial compatibility with electrodesand safety.

A lithium-ion battery typically includes a separator and/or electrolytebetween an anode and a cathode. In one class of batteries, theseparator, cathode and anode materials are individually formed intosheets or films. Sheets of the cathode, separator and anode aresubsequently stacked or rolled with the separator separating the cathodeand anode (e.g., electrodes) to form the battery. Typical electrodesinclude electro-chemically active material layers on electricallyconductive metals (e.g., aluminum and copper). Films can be rolled orcut into pieces which are then layered into stacks. The stacks are ofalternating electro-chemically active materials with the separatorbetween them.

Si is one of the most promising anode materials for Li-ion batteries dueto its high specific gravimetric and volumetric capacity (3579 mAh/g and2194 mAh/cm³ vs. 372 mAh/g and 719 mAh/cm³ for graphite), and lowlithiation potential (<0.4 V vs. Li/Li⁺). Among the various cathodespresently available, layered lithium transition-metal oxides such asNi-rich Li[Ni_(x)Co_(y)Mn(Al)_(1-x-y)]O₂ (NCM or NCA) are the mostpromising ones due to their high theoretical capacity (— 280 mAh/g) andrelatively high average operating potential (3.6 V vs Li/Li⁺). Inaddition to Ni-rich NCM or NCA cathode, LiCoO₂ (LCO) is also a veryattractive cathode material because of its relatively high theoreticalspecific capacity of 274 mAh g⁻¹, high theoretical volumetric capacityof 1363 mAh cm³, low self-discharge, high discharge voltage, and goodcycling performance. Coupling Si anodes with high-voltage Ni-rich NCM(or NCA) or LCO cathodes can deliver more energy than conventionalLi-ion batteries with graphite-based anodes, due to the high capacity ofthese new electrodes. However, both Si-based anodes and high-voltage Nirich NCM (or NCA) or LCO cathodes face formidable technologicalchallenges, and long-term cycling stability with high-Si anodes pairedwith NCM or NCA cathodes has yet to be achieved.

For anodes, silicon-based materials can provide significant improvementin energy density. However, the large volumetric expansion (>300%)during the Li alloying/dealloying processes can lead to disintegrationof the active material and the loss of electrical conduction paths,thereby reducing the cycling life of the battery. In addition, anunstable solid electrolyte interphase (SEI) layer can develop on thesurface of the cycled anodes, and leads to an endless exposure of Siparticle surfaces to the liquid electrolyte. This results in anirreversible capacity loss at each cycle due to the reduction at the lowpotential where the liquid electrolyte reacts with the exposed surfaceof the Si anode. In addition, oxidative instability of the conventionalnon-aqueous electrolyte takes place at voltages beyond 4.5 V, which canlead to accelerated decay of cycling performance. Because of thegenerally inferior cycle life of Si compared to graphite, only a smallamount of Si or Si alloy is used in conventional anode materials.

The NCM (or NCA) or LCO cathode usually suffers from an inferiorstability and a low capacity retention at a high cut-off potential. Thereasons can be ascribed to the unstable surface layer's gradualexfoliation, the continuous electrolyte decomposition, and thetransition metal ion dissolution into electrolyte solution. The majorlimitations for LCO cathode are high cost, low thermal stability, andfast capacity fade at high current rates or during deep cycling. LCOcathodes are expensive because of the high cost of Co. Low thermalstability refers to exothermic release of oxygen when a lithium metaloxide cathode is heated. In order to make good use of Si anode/NCM orNCA cathode-, and Si anode/LCO cathode-based Li-ion battery systems, theaforementioned barriers need to be overcome.

One strategy for overcoming these barriers includes exploring newelectrolyte additives in order to make good use of Si anode/NCM or NCAcathode-, and Si anode/LCO cathode-based full cells. The next generationof electrolyte additives to be developed should be able to form auniform, stable SEI layer on the surface of Si anodes. This layer shouldhave low impedance and be electronically insulating, but ionicallyconductive to Li-ion. Additionally, the SEI layer formed by the additiveshould have excellent elasticity and mechanical strength to overcome theproblem of expansion and shrinkage of the Si anode volume. On thecathode side, the ideal additives should be oxidized preferentially tothe solvent molecule in the bare electrolyte, resulting in a protectivecathode electrolyte interphase (CEI) film formed on the surface of theNi-rich NCM (or NCA) and LCO cathodes. At the same time, it should helpalleviate the dissolution phenomenon of transition metal ions anddecrease surface resistance on cathode side. In addition, they couldhelp improve the physical properties of the electrolyte such as ionicconductivity, viscosity, and wettability.

SUMMARY

In some aspects, energy storage devices are provided. In someembodiments, the energy storage device includes a first electrode and asecond electrode, wherein at least one of the first electrode and thesecond electrode is a Si-based electrode. In some embodiments, theenergy storage device includes a separator between the first electrodeand the second electrode. In some embodiments, the energy storage deviceincludes an electrolyte. In some embodiments, the energy storage deviceincludes at least one electrolyte additive comprising a compound ofFormula (A):

In some embodiments, R₁ is selected from the group consisting of a C1-C8alkyl substituted by F, an alkoxy-alkyl substituted by F, andalkenyloxy-alkyl. In some embodiments, each R₂, R₃, and R₄ isindependently an —H or a C1-C8 alkyl substituted by F. In someembodiments, R₁ is C1-C10 alkyl substituted by F or —CH₂—OR₅. In someembodiments, R₅ is a C1-C10 alkyl substituted by F or a C1-C6 alkenyl.In some embodiments, each R₂, R₃, and R₄ is independently an —H or —CF₃.

In some embodiments, the second electrode is a Si-dominant electrode. Insome embodiments, the second electrode comprises a self-supportingcomposite material film. In some embodiments, the composite materialfilm comprises greater than 0% and less than about 90% by weight ofsilicon particles, and greater than 0% and less than about 90% by weightof one or more types of carbon phases, wherein at least one of the oneor more types of carbon phases is a substantially continuous phase thatholds the composite material film together such that the siliconparticles are distributed throughout the composite material film.

In some embodiments, the electrolyte further comprises fluoroethylenecarbonate (FEC). In some embodiments, the electrolyte is substantiallyfree of non-fluorine containing cyclic carbonate.

In some embodiments, the electrolyte additive is selected from the groupconsisting of 4-(Trifluoromethyl)-1,3-dioxolan-2-one (TFPC),4,4-Bis(trifluoromethyl)-1,3-dioxolan-2-one (including cis, trans andracemate forms), 4,5-Bis(Trifluoromethyl)-1,3-dioxolan-2-one,1,1,2-Tris(trifluoromethyl)ethylene carbonate,Tetrakis(trifluoromethyl)ethylene carbonate,4-(Fluoromethyl)-1,3-dioxolan-2-one, 3,3-Difluoropropylene carbonate,4-(2,2,3,3,4,4,4-Heptafluorobutyl)-1,3-dioxolan-2-one,4-(2,2,3,3,4,4,5,5,5-Nonafluoropentyl)-1,3-dioxolan-2-one,4-(2,2,3,3,4,4,5,5,6,6,7,7,7-Tridecafluoroheptyl)-1,3-dioxolan-2-one,4-[(2,2,2-Trifluoroethoxy)methyl]-1,3-dioxolan one,4-[(2,2,3,3,3-Pentafluoropropoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,3,4,4,4-Heptafluorobutoxy)methyl]-1,3-dioxolan-2-one,3-[(2,2,3,3-Tetrafluoropropoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,4,4,4-Hexafluorobutoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2-Difluoroethoxy)methyl]-1,3-dioxolan-2-one,4-[(Hexafluoroisopropoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H-Perfluorohexoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,9H-Perfluorononoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,7H-Perfluoroheptoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,2H,2H-Perfluorohexoxy)methyl]-1,3-dioxolan-2-one, and4-[(4,4,5,5,5-Pentafluoropentoxy)methyl]-1,3-dioxolan-2-one.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional schematic diagram of an example of alithium-ion battery 300 implemented as a pouch cell.

FIG. 2 depicts an Arbin pulse function.

FIGS. 3A and 3B show the capacity (A) and capacity retention (B) of anembodiment of Si-dominant anode/LiCoO₂ cathode full cells, respectively.

FIGS. 4A and 4B show the average impedance before (A) and after (B)cycling of an embodiment of Si-dominant anode/LiCoO₂ cathode full cells,respectively.

FIGS. 5A and 5B show the average resistance before (A) and after (B)cycling of an embodiment of Si-dominant anode/LiCoO₂ cathode full cells,respectively.

FIGS. 6A and 6B show the average resistance after 10 s charge (A) anddischarge (B) of an embodiment of Si-dominant anode/LiCoO₂ cathode fullcells, respectively.

FIGS. 7A and 7B show the average resistance after 30 s charge (A) anddischarge (B) of an embodiment of Si-dominant anode/LiCoO₂ cathode fullcells, respectively.

DETAILED DESCRIPTION Definitions

The term “alkyl” refers to a straight or branched, saturated, aliphaticradical having the number of carbon atoms indicated. The alkyl moietymay be branched or straight chain. For example, C1-C6 alkyl includes,but is not limited to, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, etc. Otheralkyl groups include, but are not limited to heptyl, octyl, nonyl,decyl, etc. Alkyl can include any number of carbons, such as 1-2, 1-3,1-4, 1-5,1-6, 1-7,1-8, 1-9, 1-10, 1-11,1-12 2-3, 2-4, 2-5, 2-6, 3-4,3-5, 3-6, 4-5, 4-6 and 5-6. The alkyl group is typically monovalent, butcan be divalent, such as when the alkyl group links two moietiestogether.

The term “fluoro-alkyl” refers to an alkyl group where one, some, or allhydrogen atoms have been replaced by fluorine.

The term “alkylene” refers to an alkyl group, as defined above, linkingat least two other groups, i.e., a divalent hydrocarbon radical. The twomoieties linked to the alkylene can be linked to the same atom ordifferent atoms of the alkylene. For instance, a straight chain alkylenecan be the bivalent radical of —(CH₂)_(n)—, where n is 1, 2, 3, 4, 5, 6,7, 8, 9, or 10. Alkylene groups include, but are not limited to,methylene, ethylene, propylene, isopropylene, butylene, isobutylene,sec-butylene, pentylene and hexylene.

The term “alkoxy” refers to alkyl group having an oxygen atom thateither connects the alkoxy group to the point of attachment or is linkedto two carbons of the alkoxy group. Alkoxy groups include, for example,methoxy, ethoxy, propoxy, iso-propoxy, butoxy, 2-butoxy, iso-butoxy,sec-butoxy, tert-butoxy, pentoxy, hexoxy, etc. The alkoxy groups can befurther substituted with a variety of substituents described within. Forexample, the alkoxy groups can be substituted with halogens to form a“halo-alkoxy” group, or substituted with fluorine to form a“fluoro-alkoxy” group.

The term “alkenyl” refers to either a straight chain or branchedhydrocarbon of 2 to 6 carbon atoms, having at least one double bond.Examples of alkenyl groups include, but are not limited to, vinyl,propenyl, isopropenyl, 1-butenyl, 2-butenyl, isobutenyl, butadienyl,1-pentenyl, 2-pentenyl, isopentenyl, 1,3-pentadienyl, 1,4-pentadienyl,1-hexenyl, 2-hexenyl, 3-hexenyl, 1,3-hexadienyl, 1,4-hexadienyl,1,5-hexadienyl, 2,4-hexadienyl, or 1,3,5-hexatrienyl. Alkenyl groups canalso have from 2 to 3, 2 to 4, 2 to 5, 3 to 4, 3 to 5, 3 to 6, 4 to 5, 4to 6 and 5 to 6 carbons. The alkenyl group is typically monovalent, butcan be divalent, such as when the alkenyl group links two moietiestogether.

The term “alkenylene” refers to an alkenyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the alkenylene can be linked to the same atomor different atoms of the alkenylene. Alkenylene groups include, but arenot limited to, ethenylene, propenylene, isopropenylene, butenylene,isobutenylene, sec-butenylene, pentenylene and hexenylene.

The term “alkynyl” refers to either a straight chain or branchedhydrocarbon of 2 to 6 carbon atoms, having at least one triple bond.Examples of alkynyl groups include, but are not limited to, acetylenyl,propynyl, 1-butynyl, 2-butynyl, isobutynyl, sec-butynyl, butadiynyl,1-pentynyl, 2-pentynyl, isopentynyl, 1,3-pentadiynyl, 1,4-pentadiynyl,1-hexynyl, 2-hexynyl, 3-hexynyl, 1,3-hexadiynyl, 1,4-hexadiynyl,1,5-hexadiynyl, 2,4-hexadiynyl, or 1,3,5-hexatriynyl. Alkynyl groups canalso have from 2 to 3,2 to 4,2 to 5,3 to 4,3 to 5,3 to 6,4 to 5, 4 to 6and 5 to 6 carbons. The alkynyl group is typically monovalent, but canbe divalent, such as when the alkynyl group links two moieties together.

The term “alkynylene” refers to an alkynyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the alkynylene can be linked to the same atomor different atoms of the alkynylene. Alkynylene groups include, but arenot limited to, ethynylene, propynylene, butynylene, sec-butynylene,pentynylene and hexynylene.

The term “cycloalkyl” refers to a saturated or partially unsaturated,monocyclic, fused bicyclic, bridged polycyclic, or spiro ring assemblycontaining from 3 to 12, from 3 to 10, or from 3 to 7 ring atoms, or thenumber of atoms indicated. Monocyclic rings include, for example,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cyclooctyl.Bicyclic and polycyclic rings include, for example, norbornane,decahydronaphthalene and adamantane. For example, C3-C8 cycloalkylincludes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl,and norbornane. As used herein, the term “fused” refers to two ringswhich have two atoms and one bond in common. For example, in thefollowing structure, rings A and B are fused

As used herein, the term “bridged polycyclic” refers to compoundswherein the cycloalkyl contains a linkage of one or more atomsconnecting non-adjacent atoms. The following structures

are examples of “bridged” rings. As used herein, the term “spiro” refersto two rings which have one atom in common and the two rings are notlinked by a bridge. Examples of fused cycloalkyl groups aredecahydronaphthalenyl, dodecahydro-1H-phenalenyl andtetradecahydroanthracenyl; examples of bridged cycloalkyl groups arebicyclo[1.1.1]pentyl, adamantanyl, and norbornanyl; and examples ofspiro cycloalkyl groups include spiro[3.3]heptane and spiro[4.5]decane.

The term “cycloalkylene” refers to a cycloalkyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the cycloalkylene can be linked to the sameatom or different atoms of the cycloalkylene. Cycloalkylene groupsinclude, but are not limited to, cyclopropylene, cyclobutylene,cyclopentylene, cyclohexylene, and cyclooctylene.

The term “aryl” refers to a monocyclic or fused bicyclic, tricyclic orgreater, aromatic ring assembly containing 6 to 16 ring carbon atoms.For example, aryl may be phenyl, benzyl or naphthyl, preferably phenyl.Aryl groups can be mono-, di- or tri-substituted by one, two or threeradicals. Preferred as aryl is naphthyl, phenyl or phenyl mono- ordisubstituted by alkoxy, phenyl, halogen, alkyl or trifluoromethyl,especially phenyl or phenyl-mono- or disubstituted by alkoxy, halogen ortrifluoromethyl, and in particular phenyl.

The term “arylene” refers to an aryl group, as defined above, linking atleast two other groups. The two moieties linked to the arylene arelinked to different atoms of the arylene. Arylene groups include, butare not limited to, phenylene.

The term “heteroaryl” refers to a monocyclic or fused bicyclic ortricyclic aromatic ring assembly containing 5 to 16 ring atoms, wherefrom 1 to 4 of the ring atoms are a heteroatom each N, O or S. Forexample, heteroaryl includes pyridyl, indolyl, indazolyl, quinoxalinyl,quinolinyl, isoquinolinyl, benzothienyl, benzofuranyl, furanyl,pyrrolyl, thiazolyl, benzothiazolyl, oxazolyl, isoxazolyl, triazolyl,tetrazolyl, pyrazolyl, imidazolyl, thienyl, or any other radicalssubstituted, especially mono- or di-substituted, by e.g. alkyl, nitro orhalogen. Pyridyl represents 2-, 3- or 4-pyridyl, advantageously 2- or3-pyridyl. Thienyl represents 2- or 3-thienyl. Quinolinyl representspreferably 2-, 3- or 4-quinolinyl. Isoquinolinyl represents preferably1-, 3- or 4-isoquinolinyl. Benzopyranyl, benzothiopyranyl representspreferably 3-benzopyranyl or 3-benzothiopyranyl, respectively. Thiazolylrepresents preferably 2- or 4-thiazolyl, and most preferred 4-thiazolyl.Triazolyl is preferably 1-, 2- or 5-(1,2,4-triazolyl). Tetrazolyl ispreferably 5-tetrazolyl.

Preferably, heteroaryl is pyridyl, indolyl, quinolinyl, pyrrolyl,thiazolyl, isoxazolyl, triazolyl, tetrazolyl, pyrazolyl, imidazolyl,thienyl, furanyl, benzothiazolyl, benzofuranyl, isoquinolinyl,benzothienyl, oxazolyl, indazolyl, or any of the radicals substituted,especially mono- or di-substituted.

The term “heteroalkyl” refers to an alkyl group having from 1 to 3heteroatoms such as N, O and S. The heteroatoms can also be oxidized,such as, but not limited to, —S(O)— and —S(O)₂—. For example,heteroalkyl can include ethers, thioethers, alkyl-amines andalkyl-thiols.

The term “heteroalkylene” refers to a heteroalkyl group, as definedabove, linking at least two other groups. The two moieties linked to theheteroalkylene can be linked to the same atom or different atoms of theheteroalkylene.

The term “heterocycloalkyl” refers to a ring system having from 3 ringmembers to about 20 ring members and from 1 to about 5 heteroatoms suchas N, O and S. The heteroatoms can also be oxidized, such as, but notlimited to, —S(O)— and —S(O)₂—. For example, heterocycle includes, butis not limited to, tetrahydrofuranyl, tetrahydrothiophenyl, morpholino,pyrrolidinyl, pyrrolinyl, imidazolidinyl, imidazolinyl, pyrazolidinyl,pyrazolinyl, piperazinyl, piperidinyl, indolinyl, quinuclidinyl and1,4-dioxa-8-aza-spiro[4.5]dec-8-yl.

The term “heterocycloalkylene” refers to a heterocyclalkyl group, asdefined above, linking at least two other groups. The two moietieslinked to the heterocycloalkylene can be linked to the same atom ordifferent atoms of the heterocycloalkylene.

The term “optionally substituted” is used herein to indicate a moietythat can be unsubstituted or substituted by one or more substituent.When a moiety term is used without specifically indicating assubstituted, the moiety is unsubstituted.

DESCRIPTION

To overcome the current obstacles associated with developing high-energyfull-cells with Si-based anodes, the next generation of oxidation-stableelectrolytes or electrolyte additives are developed. The electrolyte orelectrolyte additives can form a stable, electronically insulating butionically conducting SEI layer on the surface of Si anodes.Additionally, these electrolytes or additives may also help modifycathode surfaces, forming stable CEI layers. These could enable theelectrochemical stability of Li-ion batteries when cycled at highervoltages and help with calendar life of the batteries. In addition, toalleviate battery safety concerns, these additives may impart anincreased thermal stability to the organic components of theelectrolyte, drive a rise in the flash point of the electrolyteformulations, increase the flame-retardant effectiveness and enhancethermal stability of SEI or CEI layers on the surface of electrodes.

In the present disclosure, the use of chemical compounds comprisingcyclic carbonate electrolyte additives for energy storage devices withSi-dominant anodes are described. Due to their unique chemicalstructures and functional groups, cyclic carbonate containingelectrolyte additives may bring the following benefits: (i) stabilizesolid/electrolyte interface film to reduce electrolyte reactions(oxidation on the NCM, NCA, or LCO cathode and reduction on the Sianode), prevent Si anode volume expansion, and protect transition metalion dissolution from NCM or NCA cathode and stabilize the subsequentstructure changes; and avoid the exothermic reaction between thereleased oxygen for LCO and organic electrolyte and enhance the thermalstability of LCO cathode; and (ii) reduce the flammability and enhancethe thermal stability of organic electrolytes and increase the safety ofelectrolyte solutions. Due to their versatility in reaction chemistryand overall stability in electrochemical environments, as well as haveexcellent flame resistance or fire retardant properties, involvingcyclic carbonate containing electrolyte additives into electrolytesolutions may help improve both overall electrochemical performance andsafety of Si anode-based Li-ion batteries.

Typical carbon anode electrodes include a current collector such as acopper sheet. Carbon is deposited onto the collector along with aninactive binder material. Carbon is often used because it has excellentelectrochemical properties and is also electrically conductive. If thecurrent collector layer (e.g., copper layer) was removed, the carbonwould likely be unable to mechanically support itself. Therefore,conventional electrodes require a support structure such as thecollector to be able to function as an electrode. The electrode (e.g.,anode or cathode) compositions described in this application can produceelectrodes that are self-supported. The need for a metal foil currentcollector is eliminated or minimized because conductive carbonizedpolymer is used for current collection in the anode structure as well asfor mechanical support. In typical applications for the mobile industry,a metal current collector is typically added to ensure sufficient rateperformance. The carbonized polymer can form a substantially continuousconductive carbon phase in the entire electrode as opposed toparticulate carbon suspended in a non-conductive binder in one class ofconventional lithium-ion battery electrodes. Advantages of a carboncomposite blend that utilizes a carbonized polymer can include, forexample, 1) higher capacity, 2) enhanced overcharge/dischargeprotection, 3) lower irreversible capacity due to the elimination (orminimization) of metal foil current collectors, and 4) potential costsavings due to simpler manufacturing.

Anode electrodes currently used in the rechargeable lithium-ion cellstypically have a specific capacity of approximately 200 milliamp hoursper gram (including the metal foil current collector, conductiveadditives, and binder material). Graphite, the active material used inmost lithium ion battery anodes, has a theoretical energy density of 372milliamp hours per gram (mAh/g). In comparison, silicon has a hightheoretical capacity of 4200 mAh/g. In order to increase volumetric andgravimetric energy density of lithium-ion batteries, silicon may be usedas the active material for the cathode or anode. Several types ofsilicon materials, e.g., silicon nanopowders, silicon nanofibers, poroussilicon, and ball-milled silicon, have also been reported as viablecandidates as active materials for the negative or positive electrodes.Small particle sizes (for example, sizes in the nanometer range)generally can increase cycle life performance. They also can displayvery high initial irreversible capacity. However, small particle sizesalso can result in very low volumetric energy density (for example, forthe overall cell stack) due to the difficulty of packing the activematerial. Larger particle sizes, (for example, sizes in the micronrange) generally can result in higher density anode material. However,the expansion of the silicon active material can result in poor cyclelife due to particle cracking. For example, silicon can swell in excessof 300% upon lithium insertion. Because of this expansion, anodesincluding silicon should be allowed to expand while maintainingelectrical contact between the silicon particles.

Cathode electrodes described herein may include metal oxide cathodematerials, such as Lithium Cobalt Oxide (LiCoO₂) (LCO), Ni-rich oxides,high voltage cathode materials, lithium-rich oxides, nickel-rich layeredoxides, lithium-rich layered oxides, high-voltage spinel oxides, andhigh-voltage polyanionic compounds. Ni-rich oxides and/or high voltagecathode materials may include NCM and NCA. One example of NCM materialincludes LiNi_(0.6)CO_(0.2)Mn_(0.2)O₂ (NCM-622). Lithium rich oxides mayinclude xLi₂MnO₃·(1−x)LiNi_(a)Co_(b)Mn_(c)O₂. Nickel-rich layered oxidesmay include LiNi_(1+x)M_(1−x)O₂ (where M=Co, Mn or Al). Lithium richlayered oxides may include LiNi_(1+x)M_(1−x)O₂ (where M=Co, Mn or Ni).High-voltage spinel oxides may include LiNi_(0.5)Mn_(1.5)O₄.High-voltage polyanionic compounds may include phosphates, sulfates,silicates, etc.

As described herein and in U.S. patent application Ser. Nos. 13/008,800and 13/601,976, entitled “Composite Materials for ElectrochemicalStorage” and “Silicon Particles for Battery Electrodes,” respectively,certain embodiments utilize a method of creating monolithic,self-supported anodes using a carbonized polymer. Because the polymer isconverted into an electrically conductive and electrochemically activematrix, the resulting electrode is conductive enough that, in someembodiments, a metal foil or mesh current collector can be omitted orminimized. The converted polymer also acts as an expansion buffer forsilicon particles during cycling so that a high cycle life can beachieved. In certain embodiments, the resulting electrode is anelectrode that is comprised substantially of active material. In furtherembodiments, the resulting electrode is substantially active material.The electrodes can have a high energy density of between about 500 mAh/gto about 1200 mAh/g that can be due to, for example, 1) the use ofsilicon, 2) elimination or substantial reduction of metal currentcollectors, and 3) being comprised entirely or substantially entirely ofactive material.

As described herein and in U.S. patent application Ser. No. 14/800,380,entitled “Electrolyte Compositions for Batteries,” the entirety of whichis hereby incorporated by reference, composite materials can be used asan anode in most conventional Li-ion batteries; they may also be used asthe cathode in some electrochemical couples with additional additives.The composite materials can also be used in either secondary batteries(e.g., rechargeable) or primary batteries (e.g., non-rechargeable). Insome embodiments, the composite materials can be used in batteriesimplemented as a pouch cell, as described in further details herein. Incertain embodiments, the composite materials are self-supportedstructures. In further embodiments, the composite materials areself-supported monolithic structures. For example, a collector may beincluded in the electrode comprised of the composite material. Incertain embodiments, the composite material can be used to form carbonstructures discussed in U.S. patent application Ser. No. 12/838,368entitled “Carbon Electrode Structures for Batteries,” the entirety ofwhich is hereby incorporated by reference. Furthermore, the compositematerials described herein can be, for example, silicon compositematerials, carbon composite materials, and/or silicon-carbon compositematerials.

In some embodiments, a largest dimension of the silicon particles can beless than about 40 μm, less than about 1 μm, between about 10 nm andabout 40 μm, between about 10 nm and about 1 μm, less than about 500 nm,less than about 100 nm, and about 100 nm. All, substantially all, or atleast some of the silicon particles may comprise the largest dimensiondescribed above. For example, an average or median largest dimension ofthe silicon particles can be less than about 40 μm, less than about 1μm, between about 10 nm and about 40 μm, between about 10 nm and about 1μm, less than about 500 nm, less than about 100 nm, and about 100 nm.The amount of silicon in the composite material can be greater than zeropercent by weight of the mixture and composite material. In certainembodiments, the mixture comprises an amount of silicon, the amountbeing within a range of from about 0% to about 90% by weight, includingfrom about 30% to about 80% by weight of the mixture. The amount ofsilicon in the composite material can be within a range of from about 0%to about 35% by weight, including from about 0% to about 25% by weight,from about 10% to about 35% by weight, and about 20% by weight. Infurther certain embodiments, the amount of silicon in the mixture is atleast about 30% by weight. Additional embodiments of the amount ofsilicon in the composite material include more than about 50% by weight,between about 30% and about 80% by weight, between about 50% and about70% by weight, and between about 60% and about 80% by weight.Furthermore, the silicon particles may or may not be pure silicon. Forexample, the silicon particles may be substantially silicon or may be asilicon alloy. In one embodiment, the silicon alloy includes silicon asthe primary constituent along with one or more other elements.

As described herein, micron-sized silicon particles can provide goodvolumetric and gravimetric energy density combined with good cycle life.In certain embodiments, to obtain the benefits of both micron-sizedsilicon particles (e.g., high energy density) and nanometer-sizedsilicon particles (e.g., good cycle behavior), silicon particles canhave an average particle size in the micron range and a surfaceincluding nanometer-sized features. In some embodiments, the siliconparticles have an average particle size (e.g., average diameter oraverage largest dimension) between about 0.1 μm and about 30 μm orbetween about 0.1 μm and all values up to about 30 μm. For example, thesilicon particles can have an average particle size between about 0.5 μmand about 25 μm, between about 0.5 μm and about 20 μm, between about 0.5μm and about 15 μm, between about 0.5 μm and about 10 μm, between about0.5 μm and about 5 μm, between about 0.5 μm and about 2 μm, betweenabout 1 μm and about 20 μm, between about 1 μm and about 15 μm, betweenabout 1 μm and about 10 μm, between about 5 μm and about 20 μm, etc.Thus, the average particle size can be any value between about 0.1 μmand about 30 μm, e.g., 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm,25 μm, and 30 μm.

The composite material can be formed by pyrolyzing a polymer precursor,such as polyamide acid. The amount of carbon obtained from the precursorcan be about 50 weight percent by weight of the composite material. Incertain embodiments, the amount of carbon from the precursor in thecomposite material is about 10% to about 25% by weight. The carbon fromthe precursor can be hard carbon. Hard carbon can be a carbon that doesnot convert into graphite even with heating in excess of 2800 degreesCelsius. Precursors that melt or flow during pyrolysis convert into softcarbons and/or graphite with sufficient temperature and/or pressure.Hard carbon may be selected since soft carbon precursors may flow andsoft carbons and graphite are mechanically weaker than hard carbons.Other possible hard carbon precursors can include phenolic resins, epoxyresins, and other polymers that have a very high melting point or arecrosslinked. In some embodiments, the amount of hard carbon in thecomposite material has a value within a range of from about 10% to about25% by weight, about 20% by weight, or more than about 50% by weight. Incertain embodiments, the hard carbon phase is substantially amorphous.In other embodiments, the hard carbon phase is substantiallycrystalline. In further embodiments, the hard carbon phase includesamorphous and crystalline carbon. The hard carbon phase can be a matrixphase in the composite material. The hard carbon can also be embedded inthe pores of the additives including silicon. The hard carbon may reactwith some of the additives to create some materials at interfaces. Forexample, there may be a silicon carbide layer between silicon particlesand the hard carbon.

In certain embodiments, graphite particles are added to the mixture.Advantageously, graphite can be an electrochemically active material inthe battery as well as an elastic deformable material that can respondto volume change of the silicon particles. Graphite is the preferredactive anode material for certain classes of lithium-ion batteriescurrently on the market because it has a low irreversible capacity.Additionally, graphite is softer than hard carbon and can better absorbthe volume expansion of silicon additives. In certain embodiments, alargest dimension of the graphite particles is between about 0.5 micronsand about 20 microns. All, substantially all, or at least some of thegraphite particles may comprise the largest dimension described herein.In further embodiments, an average or median largest dimension of thegraphite particles is between about 0.5 microns and about 20 microns. Incertain embodiments, the mixture includes greater than 0% and less thanabout 80% by weight of graphite particles. In further embodiments, thecomposite material includes about 40% to about 75% by weight graphiteparticles.

In certain embodiments, conductive particles which may also beelectrochemically active are added to the mixture. Such particles canenable both a more electronically conductive composite as well as a moremechanically deformable composite capable of absorbing the largevolumetric change incurred during lithiation and de-lithiation. Incertain embodiments, a largest dimension of the conductive particles isbetween about 10 nanometers and about 7 millimeters. All, substantiallyall, or at least some of the conductive particles may comprise thelargest dimension described herein. In further embodiments, an averageor median largest dimension of the conductive particles is between about10 nm and about 7 millimeters. In certain embodiments, the mixtureincludes greater than zero and up to about 80% by weight conductiveparticles. In further embodiments, the composite material includes about45% to about 80% by weight conductive particles. The conductiveparticles can be conductive carbon including carbon blacks, carbonfibers, carbon nanofibers, carbon nanotubes, graphite, graphene, etc.Many carbons that are considered as conductive additives that are notelectrochemically active become active once pyrolyzed in a polymermatrix. Alternatively, the conductive particles can be metals or alloysincluding copper, nickel, or stainless steel.

The composite material may also be formed into a powder. For example,the composite material can be ground into a powder. The compositematerial powder can be used as an active material for an electrode. Forexample, the composite material powder can be deposited on a collectorin a manner similar to making a conventional electrode structure, asknown in the industry.

In some embodiments, the full capacity of the composite material may notbe utilized during use of the battery to improve battery life (e.g.,number charge and discharge cycles before the battery fails or theperformance of the battery decreases below a usability level). Forexample, a composite material with about 70% by weight siliconparticles, about 20% by weight carbon from a precursor, and about 10% byweight graphite may have a maximum gravimetric capacity of about 2000mAh/g, while the composite material may only be used up to a gravimetriccapacity of about 550 to about 850 mAh/g. Although, the maximumgravimetric capacity of the composite material may not be utilized,using the composite material at a lower capacity can still achieve ahigher capacity than certain lithium ion batteries. In certainembodiments, the composite material is used or only used at agravimetric capacity below about 70% of the composite material's maximumgravimetric capacity. For example, the composite material is not used ata gravimetric capacity above about 70% of the composite material'smaximum gravimetric capacity. In further embodiments, the compositematerial is used or only used at a gravimetric capacity below about 50%of the composite material's maximum gravimetric capacity or below about30% of the composite material's maximum gravimetric capacity.

Electrolyte

An electrolyte for a lithium ion battery can include a solvent and alithium ion source, such as a lithium-containing salt. The compositionof the electrolyte may be selected to provide a lithium ion battery withimproved performance. In some embodiments, the electrolyte may containan electrolyte additive. As described herein, a lithium ion battery mayinclude a first electrode, a second electrode, a separator between thefirst electrode and the second electrode, and an electrolyte in contactwith the first electrode, the second electrode, and the separator. Theelectrolyte serves to facilitate ionic transport between the firstelectrode and the second electrode. In some embodiments, the firstelectrode and the second electrode can refer to anode and cathode orcathode and anode, respectively.

In some embodiments, the electrolyte for a lithium ion battery mayinclude a solvent comprising a fluorine-containing component, such as afluorine-containing cyclic carbonate, a fluorine-containing linearcarbonate, and/or a fluoroether. In some embodiments, the electrolytecan include more than one solvent. For example, the electrolyte mayinclude two or more co-solvents. In some embodiments, at least one ofthe co-solvents in the electrolyte is a fluorine-containing compound. Insome embodiments, the fluorine-containing compound may be fluoroethylenecarbonate (FEC), 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropylether, or difluoroethylene carbonate (F2EC). In some embodiments, theco-solvent may be selected from the group consisting of FEC, ethylmethyl carbonate (EMC), 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether, difluoroethylene carbonate (F2EC),ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate(DMC), propylene carbonate (PC), and gamma-Butyrolactone (GBL). In someembodiments, the electrolyte contains FEC. In some embodiments, theelectrolyte contains both EMC and FEC. In some embodiments, theelectrolyte may further contain 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether, EC, DEC, DMC, PC, GBL, and/or F2EC orsome partially or fully fluorinated linear or cyclic carbonates, ethers,etc. as a co-solvent. In some embodiments, the electrolyte is free orsubstantially free of non-fluorine-containing cyclic carbonates, such asEC, GBL, and PC.

As used herein, a co-solvent of an electrolyte has a concentration of atleast about 10% by volume (vol %). In some embodiments, a co-solvent ofthe electrolyte may be about 20 vol %, about 40 vol %, about 60 vol %,or about 80 vol %, or about 90 vol % of the electrolyte. In someembodiments, a co-solvent may have a concentration from about 10 vol %to about 90 vol %, from about 10 vol % to about 80 vol %, from about 10vol % to about 60 vol %, from about 20 vol % to about 60 vol %, fromabout 20 vol % to about 50 vol %, from about 30 vol % to about 60 vol %,or from about 30 vol % to about 50 vol %.

For example, in some embodiments, the electrolyte may contain afluorine-containing cyclic carbonate, such as FEC, at a concentration ofabout 10 vol % to about 60 vol %, including from about 20 vol % to about50 vol %, and from about 20 vol % to about 40 vol %. In someembodiments, the electrolyte may comprise a linear carbonate that doesnot contain flourine, such as EMC, at a concentration of about 40 vol %to about 90 vol %, including from about 50 vol % to about 80 vol %, andfrom about 60 vol % to about 80 vol %. In some embodiments, theelectrolyte may comprise 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether at a concentration of from about 10 vol% to about 30 vol %, including from about 10 vol % to about 20 vol %.

In some embodiments, the electrolyte is substantially free of cycliccarbonates other than fluorine-containing cyclic carbonates (i.e.,non-fluorine-containing cyclic carbonates). Examples ofnon-fluorine-containing carbonates include EC, PC, GBL, and vinylenecarbonate (VC).

Electrolyte Additives

In some embodiments, the electrolyte may further comprise one or moreadditives. As used herein, an additive of the electrolyte refers to acomponent that makes up less than 10% by weight (wt %) of theelectrolyte. In some embodiments, the amount of each additive in theelectrolyte may be from about 0.2 wt % to about 1 wt %, 0.1 wt % toabout 2 wt %, 0.2 wt % to about 9 wt %, from about 0.5 wt % to about 9wt %, from about 1 wt % to about 9 wt %, from about 1 wt % to about 8 wt%, from about 1 wt % to about 8 wt %, from about 1 wt % to about 7 wt %,from about 1 wt % to about 6 wt %, from about 1 wt % to about 5 wt %,from about 2 wt % to about 5 wt %, or any value in between. In someembodiments, the total amount of the additive(s) may be from about 1 wt% to about 9 wt %, from about 1 wt % to about 8 wt %, from about 1 wt %to about 7 wt %, from about 2 wt % to about 7 wt %, or any value inbetween.

Cyclic Carbonate Compound

In some embodiments, the cyclic carbonate can be a compound of Formula(A) having the structure:

In some embodiments, R₁ is selected from the group consisting of a C1-C8alkyl substituted by F, an alkoxy-alkyl substituted by F, andalkenyloxy-alkyl. In some embodiments, R₁ is selected from the groupconsisting of an alkoxy-alkyl substituted by F and alkenyloxy-alkyl. Insome embodiments, R₁ is selected from the group consisting of a C1-C8alkyl substituted by F and alkenyloxy-alkyl. In some embodiments, R₁ isselected from the group consisting of a C1-C8 alkyl substituted by F andan alkoxy-alkyl substituted by F. In some embodiments, R₁ is C1-C10alkyl substituted by F or —CH₂—OR₅. In some embodiments, R₁ is C1-C10alkyl substituted by F. In some embodiments, R₁ is —CH₂—OR₅.

In some embodiments, R₅ is a C1-C10 alkyl substituted by F or a C1-C6alkenyl. In some embodiments, R₅ is a C1-C10 alkyl substituted by F. Insome embodiments, R₅ is a C1-C6 alkenyl.

In some embodiments, each R₂, R₃, and R₄ is independently an —H or aC1-C8 alkyl substituted by F. In some embodiments, each R₂, R₃, and R₄is independently a C1-C8 alkyl substituted by F. In some embodiments,each R₂, R₃, and R₄ is an —H. In some embodiments, each R₂, R₃, and R₄is independently an —H or —CF₃. In some embodiments, each R₂, R₃, and R₄is an —H. In some embodiments, each R₂, R₃, and R₄ is a —CF₃.

The electrolyte or additive may comprise a cyclic carbonate. In someembodiments, the additive may be an additive chemical compoundcomprising cyclic carbonate. In some embodiments, the cyclic carbonatemay be included in the electrolyte as a co-solvent. In otherembodiments, a cyclic carbonate may be included in the electrolyte as anadditive. For example, the electrolyte may contain a cyclic carbonate asa co-solvent at a concentration of about 10 vol % or more. In otherembodiments, the electrolyte may contain a cyclic carbonate compound asan additive at less than 10 weight %.

In some embodiments, the cyclic carbonate compound is selected from4-(Trifluoromethyl)-1,3-dioxolan-2-one (TFPC),4,4-Bis(trifluoromethyl)-1,3-dioxolan-2-one (including cis, trans andracemate forms), 4,5-Bis(Trifluoromethyl)-1,3-dioxolan-2-one,1,1,2-Tris(trifluoromethyl)ethylene carbonate,Tetrakis(trifluoromethyl)ethylene carbonate,4-(Fluoromethyl)-1,3-dioxolan-2-one, 3,3-Difluoropropylene carbonate,4-(2,2,3,3,4,4,4-Heptafluorobutyl)-1,3-dioxolan-2-one,4-(2,2,3,3,4,4,5,5,5-Nonafluoropentyl)-1,3-dioxolan-2-one,4-(2,2,3,3,4,4,5,5,6,6,7,7,7-Tridecafluoroheptyl)-1,3-dioxolan-2-one,4-[(2,2,2-Trifluoroethoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,3,3-Pentafluoropropoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,3,4,4,4-Heptafluorobutoxy)methyl]-1,3-dioxolan-2-one,3-[(2,2,3,3-Tetrafluoropropoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,4,4,4-Hexafluorobutoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2-Difluoroethoxy)methyl]-1,3-dioxolan-2-one,4-[(Hexafluoroisopropoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H-Perfluorohexoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,9H-Perfluorononoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,7H-Perfluoroheptoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,2H,2H-Perfluorohexoxy)methyl]-1,3-dioxolan-2-one,4-[(4,4,5,5,5-Pentafluoropentoxy)methyl]-1,3-dioxolan-2-one, and theircorresponding partially-, or perfluoroalkyl-substituted ethylenecarbonates as well as other partially- or per-fluorine-containingheterocyclic carbonates

Example structures of cyclic carbonate compounds and are shown below:

In some embodiments, a lithium-containing salt for a lithium ion batterymay comprise lithium hexafluorophosphate (LiPF₆). In some embodiments, alithium-containing salt for a lithium ion battery may comprise one ormore of lithium tetrafluoroborate (LiBF₄), lithium hexafluoroarsenatemonohydrate (LiAsF₆), lithium perchlorate (LiClO₄), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithiumbis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB),lithium difluoro(oxalate)borate (LiDFOB), lithium triflate (LiCF₃SO₃),lithium tetrafluorooxalato phosphate (LTFOP), lithium difluorophosphate(LiPO₂F₂), lithium pentafluoroethyltrifluoroborate (LiFAB), and lithium2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), etc. In someembodiments, the electrolyte can have a salt concentration of about 1moles/L (M).

These electrolyte additives, along with the electrolytes, can be reducedor self-polymerize on the surface of Si anode to form a SEI layer thatcan reduce or prevent the crack and/or the continuous reduction ofelectrolyte solutions as the silicon containing anode expands andcontracts during cycling. Furthermore, these electrolyte additives,along with the electrolyte solvents, may be oxidized on a cathodesurface to form a CEI layer that can suppress or minimize furtherdecomposition of the electrolyte on the surface of the cathode. Withoutbeing bound to the theory or mode of operation, it is believed that thepresence of cyclic carbonates in the electrolyte can result in a SEIand/or CEI layer on the surface of electrodes with improved performance.An SEI layer comprising a cyclic carbonate compound may demonstrateimproved chemical stability and increased density, for example, comparedto SEI layers formed by electrolytes without additives or withtraditional additives. As such, the change in thickness and surfacereactivity of the interface layer are limited, which may in turnfacilitate reduction in capacity fade and/or generation of excessivegaseous byproducts during operation of the lithium ion battery. A CEIlayer comprising a cyclic carbonate compound may demonstrate may helpminimize the transition metal ion dissolutions and structure changes oncathode side and may provide favorable kinetics resulting in improvedcycling stability and rate capability. In some embodiments, electrolytesolvents comprising cyclic carbonate may be less flammable and moreflame retardant.

In some embodiments, a lithium ion battery comprising an electrolytecomposition according to one or more embodiments described herein, andan anode having a composite electrode film according to one or moreembodiments described herein, may demonstrate reduced gassing and/orswelling at about room temperature (e.g., about 20° C. to about 25° C.)or elevated temperatures (e.g., up to temperatures of about 85° C.),increased cycle life at about room temperature or elevated temperatures,and/or reduced cell growth/electrolyte consumption per cycle, forexample compared to lithium ion batteries comprising conventionallyavailable electrolyte compositions in combination with an anode having acomposite electrode film according to one or more embodiments describedherein. In some embodiments, a lithium ion battery comprising anelectrolyte composition according to one or more embodiments describedherein and an anode having a composite electrode film according to oneor more embodiments described herein may demonstrate reduced gassingand/or swelling across various temperatures at which the battery may besubject to testing, such as temperatures between about −20° C. and about130° C. (e.g., compared to lithium ion batteries comprisingconventionally available electrolyte compositions in combination with ananode having a composite electrode film according to one or moreembodiments described herein).

Gaseous byproducts may be undesirably generated during batteryoperation, for example, due to chemical reactions between theelectrolyte and one or more other components of the lithium ion battery,such as one or more components of a battery electrode. Excessive gasgeneration during operation of the lithium ion battery may adverselyaffect battery performance and/or result in mechanical and/or electricalfailure of the battery. For example, undesired chemical reactionsbetween an electrolyte and one or more components of an anode may resultin gas generation at levels which can mechanically (e.g., structuraldeformation) and/or electrochemically degrade the battery. In someembodiments, the composition of the anode and the composition of theelectrolyte can be selected to facilitate desired gas generation.

Energy Storage Device

The electrolytes and electrolyte additives described herein may beadvantageously utilized within an energy storage device. In someembodiments, energy storage devices may include batteries, capacitors,and battery-capacitor hybrids. In some embodiments, the energy storagedevice comprise lithium. In some embodiments, the energy storage devicemay comprise at least one electrode, such as an anode and/or cathode. Insome embodiments, at least one electrode may be a Si-based electrode. Insome embodiments, the Si-based electrode is a Si-dominant electrode,where silicon is the majority of the active material used in theelectrode (e.g., greater than 50% silicon). In some embodiments, theenergy storage device comprises a separator. In some embodiments, theseparator is between a first electrode and a second electrode.

In some embodiments, the energy storage device comprises an electrolyte.In some embodiments, the electrolyte comprises a solvent, solventadditive and/or compound as described previously herein. For example, insome embodiments, the electrolyte comprises a cyclic carbonate compoundas described previously herein.

Pouch Cell

As described herein, a battery can be implement as a pouch cell. FIG. 1shows a cross-sectional schematic diagram of an example of a lithium ionbattery 300 implemented as a pouch cell, according to some embodiments.The battery 300 comprises an anode 316 in contact with a negativecurrent collector 308, a cathode 304 in contact with a positive currentcollector 310, a separator 306 disposed between the anode 316 and thecathode 304. In some embodiments, a plurality of anodes 316 and cathode304 may be arranged into a stacked configuration with a separator 306separating each anode 316 and cathode 304. Each negative currentcollector 308 may have one anode 316 attached to each side; eachpositive current collector 310 may have one cathode 304 attached to eachside. The stacks are immersed in an electrolyte 314 and enclosed in apouch 312. The anode 302 and the cathode 304 may comprise one or morerespective electrode films formed thereon. The number of electrodes ofthe battery 300 may be selected to provide desired device performance.

With further reference to FIG. 1 , the separator 306 may comprise asingle continuous or substantially continuous sheet, which can beinterleaved between adjacent electrodes of the electrode stack. Forexample, the separator 306 may be shaped and/or dimensioned such that itcan be positioned between adjacent electrodes in the electrode stack toprovide desired separation between the adjacent electrodes of thebattery 300. The separator 306 may be configured to facilitateelectrical insulation between the anode 302 and the cathode 304, whilepermitting ionic transport between the anode 302 and the cathode 304. Insome embodiments, the separator 306 may comprise a porous material,including a porous polyolefin material.

The lithium ion battery 300 may include an electrolyte 314, for examplean electrolyte having a composition as described herein. The electrolyte314 is in contact with the anode 302, the cathode 304, and the separator306.

With continued reference to FIG. 1 , the anode 302, cathode 304 andseparator 306 of the lithium ion battery 300 may be enclosed in ahousing comprising a pouch 312. In some embodiments, the pouch 312 maycomprise a flexible material. For example, the pouch 312 may readilydeform upon application of pressure on the pouch 312, including pressureexerted upon the pouch 312 from within the housing. In some embodiments,the pouch 312 may comprise aluminum. For example, the pouch 312 maycomprise a laminated aluminum pouch.

In some embodiments, the lithium ion battery 300 may comprise an anodeconnector (not shown) and a cathode connector (not shown) configured toelectrically couple the anodes and the cathodes of the electrode stackto an external circuit, respectively. The anode connector and a cathodeconnector may be affixed to the pouch 312 to facilitate electricalcoupling of the battery 300 to an external circuit. The anode connectorand the cathode connector may be affixed to the pouch 312 along one edgeof the pouch 312. The anode connector and the cathode connector can beelectrically insulated from one another, and from the pouch 312. Forexample, at least a portion of each of the anode connector and thecathode connector can be within an electrically insulating sleeve suchthat the connectors can be electrically insulated from one another andfrom the pouch 312.

EXAMPLES

The below example devices and processes for device fabrication generallydescribed below, and the performances of lithium ion batteries withdifferent electrolytes and electrolyte additives are evaluated.

In the examples below, the four IR fields are values calculated by anArbin pulse function that is depicted in FIG. 2 , which calculates theaverage IR of 10 pulses, wherein: B_IR_Res: T₁=100 ms, performed at thebeginning of discharge (cell in charged state at end of rest period);E_IR_Res: T₁=100 ms, performed at the end of discharge (cell indischarged state at end of rest period); and 5-layer cells:I₀+I_(IR)=−100 mA, I₀−I_(IR)=−250 mA.

Example 1

The batteries shown in FIGS. 3A-7B are Si-dominant anode and LiCoO₂cathode 5 layer pouch cells. The Si-dominant anodes contain about 80 wt% Si, 5 wt % graphite and 15 wt % glass carbon (from resin), and arelaminated on 15 μm Cu foil. The average loading is about 3.8 mg/cm². Thecathodes contain about 97 wt % LiCoO₂, 1 wt % Super P and 2 wt %PVDF5130, and are laminated on 15 μm Al foil. The average loading isabout 28 mg/cm². The electrolytes of the control cells contain 1M LiPF₆in FEC/EMC ( 3/7 wt %), while the electrolytes of the cells of oneembodiment contain 1M LiPF₆ in FEC/EMC ( 3/7 wt %) and an electrolyteadditive of 2 wt % TFPC.

In the examples shown in FIGS. 3A-7B, the long-term cycling for bothcontrol and TFPC additive-containing cells include: (i) At the 1^(st)cycle, charge at 0.5 C to 4.3 V for 5 hours, rest 5 minutes, 1 ms IR,100 ms IR, discharge at 0.2 C to 2.75 V, rest 5 minutes, 1 ms IR, 100 msIR; and (ii) from the 2^(nd) cycle, charge at 0.5 C to 4.3 V until 0.05C, rest 5 minutes, 1 ms IR, 100 ms IR, discharge at 0.5 to 3.3 V, rest 5minutes, 1 ms IR, 100 ms IR. After each 49 cycles, the test conditionsin the 1^(st) cycle were repeated.

In addition, both control and TFPC-containing cells were formatted for 6cycles at the following conditions before long-term cycling: (i) At the1^(st) cycle, Rest 5 minutes, charge at 0.025 C to 25% nominal capacity,charge at 0.2 C to 4.3 V until 0.05 C, rest 5 minutes, discharge at 0.2C to 3.3 V, rest 5 minutes; and (ii) from 2^(nd) to 6^(th) cycles,charge at 0.5 C to 4.3 V until 0.05 C, rest 5 minutes, discharge at 0.5C to 3.3 V, rest 5 minutes.

FIG. 3A demonstrates the capacity and FIG. 3B demonstrates the capacityretention of a control battery (shown as a dotted line) and a battery ofone embodiment with 2 wt % TFPC (shown as a solid line). The results ofFIGS. 3A and 3B demonstrate that the TFPC additive-containingelectrolyte-based system has a better capacity and capacity retentionthan the control system after about 200 cycles at 0.5 C/0.5Ccharge/discharge processes.

FIG. 4A demonstrates the average impedance before cycling and FIG. 4Bdemonstrates the average impedance after cycling of a control battery(shown as a dotted line), and a battery of one embodiment with 2 wt %TFPC (shown as a solid line). The results of FIGS. 4A and 4B demonstratethat the TFPC additive-containing electrolyte system has a lowerimpedance after about 200 cycles than the control system.

FIG. 5A demonstrates the average resistance before cycling and FIG. 5Bdemonstrates the average resistance after cycling of a control battery(shown as a dotted line), and a battery of one embodiment with 2 wt %TFPC (shown as a solid line). The results of FIGS. 5A and 5B demonstratethat the TFPC additive-containing electrolyte system has a lowerresistance than the control system after about 200 cycles.

FIG. 6A demonstrates the average resistance after 10 s charge and FIG.6B demonstrates the average resistance after 10 s discharge processes ofa control battery (shown as a dotted line), and a battery of oneembodiment with 2 wt % TFPC (shown as a solid line). The results ofFIGS. 6A and 6B demonstrate that the TFPC additive-containingelectrolyte system has a lower resistance after 10 s charge/dischargeprocesses than the control system after about 200 cycles.

FIG. 7A demonstrates the average resistance after 30 s charge and FIG.7B demonstrates the average resistance after 30 s discharge processes ofa control battery (shown as a dotted line), and a battery of oneembodiment with 2 wt % TFPC (shown as a solid line). The results ofFIGS. 7A and 7B demonstrate that the TFPC additive-containingelectrolyte system has a lower resistance after 30 s charge/dischargeprocesses than the control system after about 200 cycles.

Example 2

In other embodiments not shown, the electrolytes of the cells contain 1MLiPF₆ in FEC/EMC ( 3/7 wt %) with 5 wt % TFPC. In other embodiments notshown, the electrolytes of the cells contain 1M LiPF₆ in FEC/HFDEC/EMC(3/3.5/3.5 wt %) with 2 wt % TFPC. In other embodiments not shown, theelectrolytes of the cells contain 1M LiPF₆ in FEC/HFDEC/EMC (3/3.5/3.5wt %) with 5 wt % TFPC. These examples also demonstrated improvedbattery functions when TFPC was used as an additive as compared tocontrols.

Various embodiments have been described above. Although the inventionhas been described with reference to these specific embodiments, thedescriptions are intended to be illustrative and are not intended to belimiting. Various modifications and applications may occur to thoseskilled in the art without departing from the true spirit and scope ofthe invention as defined in the appended claims.

What is claimed is:
 1. An energy storage device comprising: a firstelectrode and a second electrode, wherein at least one of the firstelectrode and the second electrode is a Si-based electrode; a separatorbetween the first electrode and the second electrode; an electrolyte;and at least one electrolyte additive comprising a compound selectedfrom the group consisting of 4,4-Bis(trifluoromethyl)-1,3-dioxolan-2-one(including cis, trans and racemate forms),4,5-Bis(Trifluoromethyl)-1,3-dioxolan-2-one,1,1,2-Tris(trifluoromethyl)ethylene carbonate,Tetrakis(trifluoromethyl)ethylene carbonate,4-(Fluoromethyl)-1,3-dioxolan-2-one, 3,3-Difluoropropylene carbonate,4-(2,2,3,3,4,4,4-Heptafluorobutyl)-1,3-dioxolan-2-one,4-(2,2,3,3,4,4,5,5,5-Nonafluoropentyl)-1,3-dioxolan-2-one,4-(2,2,3,3,4,4,5,5,6,6,7,7,7-Tridecafluoroheptyl)-1,3-dioxolan-2-one,4-[(2,2,2-Trifluoroethoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,3,3-Pentafluoropropoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,3,4,4,4-Heptafluorobutoxy)methyl]-1,3-dioxolan-2-one,3-[(2,2,3,3-Tetrafluoropropoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2,3,4,4,4-Hexafluorobutoxy)methyl]-1,3-dioxolan-2-one,4-[(2,2-Difluoroethoxy)methyl]-1,3-dioxolan-2-one,4-[(Hexafluoroisopropoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H-Perfluorohexoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,9H-Perfluorononoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,7H-Perfluoroheptoxy)methyl]-1,3-dioxolan-2-one,4-[(1H,1H,2H,2H-Perfluorohexoxy)methyl]-1,3-dioxolan-2-one, and4-[(4,4,5,5,5-Pentafluoropentoxy)methyl]-1,3-dioxolan-2-one.
 2. Theenergy storage device of claim 1, wherein the second electrode is aSi-dominant electrode.
 3. The energy storage device of claim 1, whereinthe second electrode comprises a self-supporting composite material. 4.The energy storage device of claim 5, wherein the composite materialcomprises: greater than 0% and less than about 90% by weight of siliconparticles, and greater than 0% and less than about 90% by weight of oneor more types of carbon phases, wherein at least one of the one or moretypes of carbon phases is a substantially continuous phase that holdsthe composite material together such that the silicon particles aredistributed throughout the composite material.
 5. The energy storagedevice of claim 1, wherein the electrolyte further comprisesfluoroethylene carbonate (FEC).
 6. The energy storage device of claim 5,wherein the electrolyte is substantially free of non-fluorine containingcyclic carbonate.